78 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



mentioned Lake Temiscaming specimen. The corallites are hexagonal, 

 about 2 mm. in diameter, and the interspaces triangular. In this speci- 

 men the coral is well shown on a weathered surface, but below the surface 

 the structure is not sufficiently preserved to reveal anything in longitu- 

 dinal or transverse sections. 



The Guelph representatives of this species have corallites about or 

 slightly over 2*5 mm. in diameter, and the interspaces are generally 

 rather irregular in shape and as a rule narrower than the corallites, 

 although their length is sometimes as much as the breadth of two coral- 

 lites, thus showing a tendency to form true meshes and to depart from 

 the typical growth of H. compacta in which no meshes are formed and 

 the corallites touch each other on every side. The corallites are circular 

 in section and have rather thick walls. The specimens available for 

 study are preserved in a light yellow dolomite which does not admit of 

 much detail of structure being made out : the presence of septal spines 

 is indicated but no tubules between the corallites have been detected. 

 The tabulae of the corallites are flat or concave and occasionally convex ; 

 from five to seven occur in a space of 5 mm. It will be thus seen that H. 

 compacta as found in the Guelph formation of Ontario is much coarser or 

 more robust than those forms found in the Niagara formation at Lake 

 Temiscaming, Ont. 



Mr. Whiteaves records the collection of this species at Gait, Ont., by 

 the Rev. A. Bell, 1846-50; at Elora, Ont., by Dr. R, Bell, 1861 and D. 

 Boyle, 1883; and at Hespeler, O., by T. C. Weston, 1867. There is 

 in the survey collection a specimen from Durham, Ont., collected by J. 

 Townsend in 1883. 



